|Wednesday, December 16|
Fundamentals and Applications of Electrodeposited Au from Pyridine-Derivative Containing Solutions
* Ian Burgess, University of Saskatchewan, Canada
Tetrachloroaurate is, by far, the most popular precursor used in the formation of gold nanoparticles. However, AuI species have been championed as potentially better precursors because of the lower energy associated with one versus three electron transfer, the larger thermodynamic driving force for the reduction of AuI compared to AuIII, and the use of AuI-complex ligands as in situ capping agents and growth directing mediators. Empirically, we have observed evidence of the spontaneous formation of a AuI species upon the addition of 4-methoxypyridine (Py/) to aqueous tetrachloroaurate (AuCl4-) solutions. In this seminar, fundamental studies of the (electro)chemistry of the tetrachloroaurate- (Py/) system are described that reveal the co-existence of both AuIII and AuI species. The observation of a slow, but spontaneous, conversion of AuIII species to AuI species is explained by demonstrating that the oxidation of the pyridine derivative drives a galvanic reaction involving a AuIII/ AuI redox couple. Electrodeposition of metallic gold onto ITO electrodes from these solutions leads to the formation of highly anisotropic nanoparticles and can be (at least partially) attributed to the disproportionation of AuI and the preferential adsorption of (Py/) on certain crystallographic facets of growing electrodeposits. The resulting gold modified substrates have excellent applications as bimodal platforms for surface enhanced vibrational spectroscopies. Dagger shaped gold particles have been electrodeposited on surfaces of conductive indium tin oxide (ITO) films. The optical extinction of these AuND@ITO substrates extends from the near-IR to long wavelength mid-infrared frequencies. AuND@ITO substrates are assessed as potential enhancing interfaces for dual modality, spectroelectrochemical, surface sensitive vibrational spectroscopy; specifically surface enhanced Raman spectroscopy (SERS) using 1064 nm excitation and attenuated total reflectance surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) using a broadband emission source.